The invention relates to a device for locking the end positions of movable switch parts and, in particular, the movable point of a frog, in which two relatively axially displaceable parts are capable of being displaced into a position coupled with each other in a positive manner in at least one direction of movement, wherein the relatively displaceable parts are comprised of a tube and a rod guided within the tube and are at least partially arranged in a stationary outer tube, whereby locking members cooperate with the relatively axially displaceable parts as well as the outer tube and are capable of being displaced in the radial direction into a locking position in a recess or inner annular groove of the outer tube.
From EP-A 603 156 a device of the above-mentioned type has already become known, in which locking members comprised of balls are pressed into their locking positions by means of stops formed by thickened rod regions, thus abutting on a full-diameter partial region of the rod within a recess of the outer tube in the locking position. The balls pass through openings of the tubes surrounding the rod and each connected to a tongue, in a manner that a relative movement of this structural component connected with the tongue, namely the tube, relative to the outer tube will be effectively prevented as the balls are being pressed into their external positions, thus effecting locking between the outer tube and the tubular structural component. In order to undo said locking, the rod will have to be displaced, which may cause the ball to fall back onto reduced-diameter regions, thus emerging from the locking position within the groove of the outer tube.
According to a proposal known from WO 98/54041, the locking device known from EP 603 156 was improved to the effect that the balls are encompassed by an expandable ring or a ring comprised of segments. This measure aims to reduce the wear of the balls otherwise taking up the high locking forces via point contacts, since the accordingly high load can now be taken up by the annular segments or the expandable ring.
Furthermore, devices for shifting the positions and elastically locking the end positions of movable switch parts are also known, which are likewise referred to as switching aids. Such switching aids comprise an axially displaceable rod and a tube surrounding the rod, in which a spring surrounding the rod is braced against stops and radially outwardly displaceably locking members are arranged, the rod including, in an axially spaced-apart manner, control stops for the radially internal position of the locking members and the tube including stops for the external position of the locking members. Departing from such switching aids, it was proposed, for instance, in wo 00/69697 to fix at least one of the control stops to the rod in a manner displaceable in the axial direction of the rod. It is thereby feasible to adapt the displacement stroke of the adjustment device to the respective requirements. In particular, it is thereby safeguarded that the resilient application force at the tongue will enter into effect independently of a respectively adjustable active displacement path in order to enable the generation of constant application forces at the tongue irrespective of the displacement stroke.
All of the known devices are only suitable for the adjustment and locking of switch tongues, wherein a piston unit is arranged between the known locking devices, the piston rod of said piston unit being a component of the locking device. Both of the locking devices with the interposed hydraulic cylinder are coupled to the two tongues and serve to move and lock the closed and open positions, respectively, of the respective tongue. In order to adjust the movable point of a frog, it is, for instance, described in DE 2 002 025 how the movable frog is being connected to an existing, known switch lock using a clamp-like catch unit. To this end, the movable frog is being embraced on its lower side in the front nose region upon interposition of a slide piece which is coupled with the rod assembly of the switch lock using a clamp-like catch unit.
Unlike the adjustment of a tongue switch, the adjustment of a movable point of a frog calls for the observance of highly precise displacement paths, since in this case the adjustment is not effected between a closed and an open position, but both end positions of the displacement path constitute closed or abutment positions. Abutment in this case must be effected in a particularly precise manner, since it is usually required that a maximum gaping of the frog point in the abutment position of only 3 mm be admissible. The invention, therefore, aims to improve a device of the initially defined kind with a view to precisely adjusting the displacement stroke and enabling precise locking of the end position. The device is to be particularly suitable for the locking of an end position of the movable point of a frog and, at the same time, readily adaptable to the distance at which the locking device is coupled to the movable frog from the frog point, and hence the necessary displacement path.
To solve this object, the configuration according to the invention essentially consists in that the outer tube is comprised of two tube parts capable of being axially displaced within each other, and that each tube part carries at least one recess or inner annular groove. The arrangement of the recesses or inner annular groove engaged by the locking members in the displaced end position on two outer tube parts capable of being axially displaced within each other provides the prerequisite for the axial displacement of the locking grooves in order to thereby adjust the displacement stroke between the two end positions corresponding to the abutment position of the movable frog. Such an adjustment will be necessary, in particular, where one and the same locking device is coupled to the movable frog at different distances from the frog point. As a rule, one or several locking devices are arranged along a movable frog point with different displacement paths being each required. In order to standardize the mode of construction of the locking device, it is therefore necessary to use a uniform device in any locking plane with the only adjustment required being that of the respectively different stroke. This is now feasible in a simple manner by the configuration of the outer tube according to the invention, which is comprised of two tube parts capable of being axially displaced within each other. As a result, it is feasible to adjust the relative positions of the recesses or locking grooves arranged on the two tube parts according to the respective requirements already at the works-side assembly of the locking device.
In a preferred manner, the tube parts are each provided with a thread and capable of being screwed into each other, it being preferred that one tube part is designed as a stationary or rotationally fast inner tube and the other tube part is designed as an outer tube capable of being axially displaced by rotation and fixed in a rotary position. One of the tube parts can, thus, be displaced axially relative to the other tube part by simple rotation, extremely precise adjustment of the displacement stroke being feasible by transforming the rotary movement into an axial displacement of the tube part. To this end, the configuration in a preferred manner is further developed such that the axially displaceable outer tube comprises recesses for the engagement of a tool intended to rotate the axially displaceable outer tube.
For the operating safety of the locking device it is necessary that the respectively adjusted axial position of the two tube parts relative to each other and the thus adjusted displacement stroke can be fixed. To this end, the configuration in a preferred manner is devised such that the axially displaceable outer tube cooperates with a flange tube and is braceable between the flange tube and the stationary or rotationally fast inner tube, wherein, furthermore, the flange tube carries an internal thread and is capable of being screwed onto an external thread of the axially displaceable outer tube. This enables the two tube parts of the outer tube to be braced relative to each other in the axial direction, and hence prevented from being rotated. The axial bracing of the two tube parts offers the advantage of achieving an extremely compact mode of construction while, at the same time, rendering the arrangement of radially extending pins superfluous for the securement of the respective rotary position of the outer tube parts. The locking device is to constitute a compact and self-contained structural unit after the works-side adjustment of the respective displacement stroke, wherein it is particularly sought that no parts readily accessible from outside be provided, which would enable an alteration of the displacement stroke adjusted by the manufacturer. In a preferred manner, the configuration is devised such that at least one screw connection is provided for the fixation of the rotary position.
In order to ensure the respective axial displaceability of the two tube parts of the outer tube, a clear cross section between the outer circumference of the tube and the inner circumference of the axially displaceable outer tube cannot be prevented. In order to safeguard the engagement of the locking members not in this clear cross section, but only in the locking grooves provided therefor, the configuration advantageously is further developed such that adjustable cheek bridges or a spacer sleeve are arranged in the clear cross section between the outer circumference of the tube and the inner circumference of the axially displaceable outer tube. The use of cheek bridges has the advantage of enabling the continuous adjustment of the displacement stroke, whereas the use of spacer sleeves merely allows for stepwise adjustment.
While, during the displacement movement of the movable frog, the forces to be taken up by a locking ball are limited by the maximally admissible displacement force, the balls usually can be stressed by a multiple in the locking position. Since such locking forces can be taken up by balls merely by point contacts, the contact points are exposed to very high loads, which may lead to inadmissible deformations. In order to ensure also the absorption of extremely high locking forces without entailing the risk of a premature functional impairment of the lock, the configuration preferably is further developed in a manner that the locking members are formed by balls which are encompassed by an expandable ring or a ring comprised of segments, that the segments or the ring, respectively, are/is resiliently held in a position with an outer diameter smaller than, or equal to, the outer diameter of the axially displaceable tube guided within the outer tube, and reach(es) into a peripheral groove of the tube, and that the balls are arranged in tube holes provided between the rod and the ring comprised of segments.